PMAA/PEG complexes

Papisov et al. (1974) performed calorimetric and potentiometric experiments to determine the thermodynamic parameters of the complex formation of PMAA and PAA with PEG. They investigated how temperature and the nature of the solvent affected the complex stability. They found that in aqueous media the enthalpy and entropy associated with the formation of the PMAA/PEG complex are positive while in an aqueous mixture of methanol both of the thermodynamic quantities become negative. The exact values are shown in Table II. The viscosities of aqueous solutions containing complexes of PMAA and PEG increase with decreasing temperature as a result of a breakdown of the complexes. 

The temperature stability of the complexes seems to be dependent on the molecular weight of the PEG chain, i.e., the larger the PEG the lower the temperature at which the complex dissociates. An important observation was that the complexation/decomplexation phenomenon was reversible by changing the temperature of the system. The positive values of the thermodynamic parameters as well as the experimental observations clearly indicate the important role of hydrophobic interactions in the stabilization of the PMAA/PEG complexes. Since PAA is considerably more hydrophilic than PMAA, hydrophobic interactions do not play an important role in stabilizing the PAA/PEG complexes. This is represented by the much... 

Fig. 4. Temperature dependences of reduced viscosities (C of PMAA = 0.1 g/dl) of PMAA-PEG complexes in water Mv of PMAA = 5 x 10s Mv of PEG = 5 X 103 (2), 2 x lO (3) curve 1 denotes PMAA in the absence of PEG33>...

The dilution of solutions33 containing equimolar ratios of monomer units of the complex components results in the dissociation of the complexes of PMAA with low-molecular weight PEG. The reduced viscosity of solutions rapidly increases, which indicates the existence of the equilibrium PMAA + PEG complex. In the case of a relatively high-molecular weight PEG, the PMAA macromolecules are firmly connected with PEG and at the dilution of aqueous solution, an increase of the reduced viscosity typical of polyelectrolytes does not occur, i.e. the complex does not dissociate. The absence of temperature dependence of the relative viscosity in the temperature range 15-40 °C is indicative of the stability of this complex (Fig. 4). 

Fig. 29. Dependence of the degree of completion X of the exchange reaction between PMAA-PEG complex + PMAA PMAA -PEG complex + PMAA on the degree of polymerization of PEG, n. Time is 1000 (1) and 100 (2) minutes123 ...

Selectivity of complex formation was used for the separation of components of the polyelectrolyte complex119 interacting with nonionic polymers. The PMAA-PDMAEMA complex was separated into macromolecular components at pH 2.5 by adding PEG in a quantity necessary for binding all the PMAA molecules in the complex. Analysis of the precipitated PMAA-PEG complex shows that the preripita-tion is complete and that the complex does not practically contain the polymer base. 

PEG, PAA-PEG complexes is much higher than that of the initial high molecular weight components. Sedimentation coefficients of PMAA-PEG complexes in water are 20-25 s/g, indicating a high compactness of the particles. Two types of distribution are possible ... 

The effect of intermacromolecular interactions on the IMM of the polymer chains forming PC has been investigated in detail for PMAA-PEG complexes. Data... 

Figure 4.19. Temperature dependence of reduced viscosities of PMAA abd PMAA-PEG complexes in water [103] 1) PMAA 2) PMAA-PEG, Mw of PEG = 2000 3) PMAA-PEG, Mw of PEG = 20 000. [PEG]/[PMAA] = 1.0 (per repeating unit) PMAA = 0.05 g/100 ml.

Fig.-14. Temperature dependences of reduced viscosities of PMAA and PMAA-PEG complexes in water (1) PMAA ...

The values of 0 for various PMAA-PEG complexes as a function of temperature are summarized in Table 2 As predicted from the viscosity measurements, PEG with a molecular weight of 1000 or lower has very low 0 values, whereas for PEG with molecular weights of2000 or 3000 0 increases rapidly above a certain temperature. Complexes prepared from PEG with molecular weights of 7500 and 20,000 have large 0 values nearly equal to 1,0 which are almost insensitive to temperature changes. 

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